1. Field
This disclosure relates to mixer circuits.
2. Description of Related Art
Mixer circuits are commonly used in a number of applications. As one example, they are often used in radio frequency (RF) applications for up-converting (up-mixing) or down-converting (down-mixing). In this context, up-converting is the process of mixing a baseband signal (such as a differential baseband signal) with an RF signal (such as a differential RF signal) that is generated by a local oscillator (LO) circuit that operates in the RF range. Alternatively, an intermediate frequency (IF) may also be used in the mixing process. In such a situation, multiple mixing stages may be used to convert between baseband frequencies and RF frequencies. For purposes of this disclosure, the term “baseband” will be used to describe the source signal that is being mixed and/or unmixed with an RF signal. It will be appreciated, however, that in such applications an IF signal could be used in place of a baseband signal.
An up-mixing (up-conversion) process generates a mixed RF signal with the baseband signal information included with (mixed with) an RF signal generated by the LO. Down-converting is the process of separating (un-mixing) the baseband signal from the mixed RF signal. This is typically accomplished by using a mixer circuit with a local oscillator of substantially an identical frequency as was used to mix the mixed RF signal.
One typical type of mixer circuit that is used in such application is a passive mixer circuit, which may be implemented using a complementary-metal-oxide semiconductor circuit fabrication process (e.g. on an integrated circuit). However, such circuits have certain drawbacks. For instance, the LO signal used in such circuits must have an amplitude that is on the order of the operating voltage for the particular technology with which the mixer circuit is implemented. Designing and manufacturing such LO circuits that operate at a desired frequency (e.g., in the range of 1 to 5 GHz), have sufficient signal amplitude (“high amplitude LO circuits”) and have adequate timing characteristics (e.g., switching times) is difficult and may be prohibitive for certain applications.
For instance, the high power consumption of such LO circuits may be incompatible with battery operated consumer devices due the reduction of battery life resulting from such power consumption. Further, the cost of manufacturing such LO circuits may also be prohibitive for use in certain products, such as commodity electronics (e.g., due to the integrated circuit area consumed by such circuits). Still further, design of such high amplitude LO circuits is difficult, time intensive and, therefore, expensive.
An additional drawback of such high amplitude LO circuits is that noise from the drivers included in the circuit may be communicated into other circuit stages with which the mixer circuit is coupled. For instance, in a situation where such a passive mixer is used in an RF receiver (e.g., in a down-mixing application), noise from the LO circuit drivers may be especially problematic, as such circuits tend to be susceptible to the effects of weak signals (e.g., noise). In such applications, noise from the LO drivers may adversely impact the performance of a mixer circuit that is being driven by the LO circuit drivers, as well the performance of circuits that are coupled with the mixer circuit.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.